The present invention relates to a method for manufacturing a metallic stamper and a metallic stamper fabricated by the manufacturing method and, a method for manufacturing substrates of optical disks with the use of the stamper and optical disks fabricated by the manufacturing method. The substrates of the optical disks are used for CDs(Compact Disks), DVD(Digital Versatile Disk)-ROMs, DVD-RAMS, etc.
A conventional method for producing optical disk substrates will be described.
One example of the conventional manufacturing methods for the optical disk is disclosed in the xe2x80x9cMaterial by the Electricity Studies Magnetics Meeting (on pages 29-37, 1996)xe2x80x9d, which is a manufacturing method for high-recording-density optical disks based on a Deep Groove method. A manufacturing method with using dry etching for a master is reported in the Material.
FIGS. 4A-4F show a conventional art of production procedures for the master by dry etching. In FIGS. 4A-4F, 31a is a quartz substrate to be a master and 32 is a pattern of resist as an etching mask formed by exposure and development by a laser cutting machine. 31b is the quartz substrate from which the resist is removed after dry etching. 34 is a stamper made of Ni comprising an Ni coat 34a formed by sputtering and an Ni main body portion 34b formed by electroforming, so called a plating. 35 is an optical disk substrate molded of polycarbonate.
Hereinbelow is discussed the production process of the master with using dry etching in the manufacturing method for the optical disk substrates.
In the first place, a resist is provided in a thickness of 140 nm on the quartz substrate 31a by a rotational application method, so called spin coating. The resist is exposed by the laser cutting machine to form a pattern of grooves and a pattern of pits, and developed, whereby the pattern of resist 32 as shown in FIG. 4A is obtained. The quartz substrate is then etched to a depth of 70 nm by dry etching with the use of a gas including oxygen and fluorine (e.g., mixed gas of CHF3 and O2) while the pattern of resist 32 is used as an etching mask. The resist of the pattern is removed thereafter, whereby the quartz substrate 31b having depressions and projections on a surface thereof as indicated in FIG. 4B is obtained. The depressions formed on the surface of the quartz substrate 31b form the grooves and pits on the optical disk substrate 35. After the quartz substrate 31b is cleaned, the Ni coat 34a of a thickness of 50 nm is formed on a whole area of the quartz substrate 31b by sputtering. In FIG. 4C, a whole area of the Ni coat 34a is subjected to 0.4 mm-thick Ni plating by electroforming, thereby forming the Ni main body portion 34b. The Ni stamper 34 of FIG. 4D is obtained by removing the quartz substrate 31b. With using the Ni stamper 34 as a mold, the optical disk substrate 35 of polycarbonate is molded as shown in FIGS. 4E and 4F. A recording film and a protecting film are formed on the substrate 35, and then an optical disk is completed by bonding each protecting film of two substrates 35 with an adhesive.
In the conventional method as described hereinabove, when the Ni stamper 34 is separated from the quartz substrate 31b having the grooves and pits formed by the dry etching, the quartz substrate 31b and Ni stamper 34 are subjected to friction at depressions 36 and projections 37 because of a difference of thermal expansion coefficients of the quartz substrate 31b and Ni stamper 34 and also an internal stress of the Ni coat 34a, which leads to protuberances 38 at a surface of the stamper 34 due to a difference of hardnesses of quartz and Ni as is clear from FIG. 4D. The shape of the surface of the stamper 34 is eventually transferred to the optical disk substrate 35, forming recesses 39 which invite noises on the occasion of recording and reproduction. Further, when the quartz substrate is processed by dry etching to form the projections 37 and the depressions 36 forming the grooves and pits, since each depth of the grooves and pits, that is, each depth of the depressions 36 is controlled by a time of the dry etching, high depth accuracy cannot be expected and uniformity on the etched plane and reproducibility of the etching are rendered instable, resulting in irregular noise characteristic.
In a different method for manufacturing the optical disks employed heretofore, the Ni stamper is directly formed on the resist pattern on the quartz substrate. However, it is difficult to form the resist pattern in a rectangular shape to conform to a fine pattern of the resist to attain high-density recording, and at the same time a surface of the patterned resist coat is not smooth, but rough. Thus, the noise characteristic becomes disadvantageously poor in this method as well.
The object of the present invention is therefore to provide a manufacturing method for a metallic stamper and a metallic stamper, and a manufacturing method for optical disk substrates with the use of the metallic stamper and optical disks produced by the manufacturing method, which can finely form grooves, or grooves and pits of optical disk substrates with high density, thereby realizing large-capacity optical disks and reducing a noise level. A further object of the present invention is to enhance depth accuracy in forming the grooves, or the grooves and pits with good reproducibility.
In order to accomplish the above-described objects, according to a first aspect of the present invention, there is provided a manufacturing method for a metallic stamper, which comprises:
forming a coat made of a low-hardness material onto a substrate which is to be a master, the low-hardness material having a lower hardness than metal of projections at a metallic stamper to prevent deformation of the projections on the occasion of separating a metallic portion from the master;
forming a pattern of a mask to be an etching mask onto the low-hardness material;
etching a non-masked portion not masked by the mask of the low-hardness material at least partially in a thicknesswise direction of the substrate;
after the etching, removing the mask, thereby obtaining the master;
forming the metallic portion onto the master; and
separating the metallic portion from the master, thereby obtaining the metallic stamper.
Further, the non-masked portion may be totally removed in the thicknesswise direction of the substrate so as to expose a smooth surface of the substrate, so that the smooth surface constitutes smooth top faces of the projections.
Further, a thickness of the low-hardness material formed on the substrate of the master may correspond to a depth of grooves or pits of an optical disk substrate produced with the use of the metallic stamper.
According to the first aspect of the present invention, the low-hardness material is lower in hardness than a metal forming projections of the metallic stamper, and therefore the metallic stamper is prevented from being flawed and finned when separated from the master. Thus, grooves, or grooves and pits can be formed finely with high accuracy in the optical disk substrates. When the low-hardness material is provided to be even with the grooves, or the grooves and pits of the optical disk substrate, the low-hardness material can be almost selectively etched by selecting the low-hardness material or etching-gas or etching method without etching the substrate, so that the uniformity in the depth of the grooves, or the grooves and pits at a whole area of bottom surfaces of the grooves and pits and reproducibility in forming the grooves, or the grooves and pits are enhanced. Depth accuracy of the grooves, or the grooves and pits is increased, and optical disk substrates can be manufactured with good reproducibility.
Further, according to the second aspect of the present invention, there is provided a metallic stamper which is formed with the use of the manufacturing method of the first aspect of the present invention.
Further, according to the third aspect of the present invention, there is provided a manufacturing method for optical disk substrates, comprising molding a resin with the use of the metallic stamper of the second aspect of the present invention to form an optical disk substrate.
Further, according to the fourth aspect of the present invention, there is provided an optical disk manufactured by molding resin with the use of the manufacturing method for optical disk substrates of the third aspect of the present invention.